This invention relates to a diamond-like thin film and also to a process and an apparatus for manufacturing the same. More particularly, it concerns a technique of manufacturing an excellent diamond-like thin film free from crack and/or having good surface properties.
The expression "diamond-like" as used herein encompasses the thin films in the crystallinity range from a level high enough to be regarded as diamond to a slightly lower level.
Diamond-like thin films made by the vapor phase process have high hardness and excellent wear resistance, durability, and resistance to chemicals and corrosive attacks, and provide coatings on articles of varied shapes. They are useful or promising as protective films on articles for which one or more of the above-mentioned properties are essential requirements.
The equipment for the manufacture of diamond-like thin film by the vapor phase process is available in some types. (Refer, for example, to "HYOMEN KAGAKU" (Surface Chemistry), vol. 5, No. 108 (1984), pp. 108-115, "Various methods", and to the processes disclosed in Japanese Patent Application Nos. 59376/1988 and 59377/1988.) Diamond-like thin films are extensively used as corrosion- and wear-resistant protective coatings applied to objects of varying configurations that require surface protection.
However, the conventionally made diamond-like thin films tend to crack first along the periphery and then inwardly when the thickness or hardness exceeds certain limits, independently of the type of substrate used. Thus, adequate corrosion resistance or durability is not attained by a mere increase in thickness. On the other hand, if it is made thin enough to remain uncracked, the wear resistance and other desirable properties become deficient. The crack problem is presumably attributed to the fact that some ununiformity of conditions at the time of film forming, including the high-temperature heating of the substrate, applies internal stresses to the film and that the harder the film the more readily the internal stresses build up.
At the present time no process is available which produces a diamond-like thin film protected against cracking through relief of such internal stresses and free from cracking despite high hardness or adequate thickness.
The diamond-like thin films made by conventional processes are aggregates of minute crystals and therefore have sharp surface irregularities and roughness. Those thin films have such low binding forces with respect to the substrates that they come off easily from the latter. They also tend to crack owing to internal stresses. Thus, they cannot serve fully effectively in applications that require resistance to corrosion and wear. They are not quite reliable, either, when used on electronic and structural materials. A particularly notable tendency is that the surface properties of the films deteriorate as the hardness increases. In addition, the surface roughness makes the film less affinitive for adhesives and coating materials.
Among the prior art processes, ionization evaporation (Patent Application Public Disclosure No. 174507/1984 and Patent Application Nos. 59376/1988, 59377/1988, 1199/1989, 15093/1989, etc.) is known as a technique of producing diamonds or diamond-like films with long range order and relatively good continuity, flatness, and smoothness. Microscopically, the technique is still unable to give a completely continuous or flat and smooth film. The surface unevenness is rather worsened because the mesh of the grid renders the ion beam distribution ununiform.
The present invention is aimed at providing a diamond-like thin film free from crack and/or having adequate thickness, plus excellent surface properties. It is also aimed at providing a process and an apparatus for producing a diamond-like thin film of this character.